FCM rxjs compatibility broken?

[zwu52]

FCM API suggests that it offers rxjs compatibility out of box. Specifically, you could do

let foregroundMessages$ = rxjs.Observable.create(function subscribe(observer) {
  messaging.onMessage(observer);
});

foregroundMessages$.subscribe({
  next: (msg) => handleForegroundMessage(msg),
  error: (err) => console.log("err: " + err),
});

However, an error is thrown:

Uncaught (in promise) TypeError: this._next is not a function
    at rt.Subscriber.next [as onMessageCallback] (rxjs.umd.js:472)
    at rt.<anonymous> (window-controller.ts:197)
    at tslib.es6.js:100
    at Object.next (tslib.es6.js:81)
    at tslib.es6.js:74
    at new Promise (<anonymous>)
    at v (tslib.es6.js:70)
    at rt.messageEventListener (window-controller.ts:188)
    at ServiceWorkerContainer.<anonymous> (window-controller.ts:47)

Came across this error here as well (angular/angularfire#2299)

[zwu52]

ref: FCM API

[Feiyang1]

Reading angular/angularfire#2299 (comment), seems it was working before 7.6.0. Any idea what changed?

[zwu52]

Finally got a chance to route back to this. I think I found the cause for this: currently window controller stores a member variable onMessageCallback which gets fed with value from nextOrObserver. Internally, if this nextOrObserver is not a callback function, we do this.onMessageCallback = nextOrObserver.next assuming the next callback is passed directly from the observer object developer provided in

{
  next: (msg) => handleForegroundMessage(msg),
  error: (err) => console.log("err: " + err),
}

However, rxjs actually does some internal operation and converts the observer into a subscriber instance, such instance should be used as a unit as it is (e.x. subscriber.next()). Trying to extract the next callback from it will result in

this.onMessageCallback = function: ƒ (value) {
           if (!this.isStopped) {
               this._next(value);
           }
       }

since next is stripped away from the generated subscriber, this._next nor this.isStopped is undefined.
I have a PR that would resolve this issue.

[hiepxanh]

perfect, I'm coming from angular/angularfire#2497 (comment) and I'm wating for your fix to update my PR